1. Technical Field
This invention is directed to the field of surgery and is specifically directed to use of heat, especially that resulting from the application of radio frequency energy, to modify the length of ligaments.
2. Background
Instability of joints between bones has long been recognized as a significant cause of disability and functional limitation in patients. For example, diarthrodial joints of the musculoskeletal system have varying degrees of intrinsic stability based on joint geometry and ligament and soft tissue investment. Diarthrodial joints are comprised of the articulation of the ends of bones and their covering of hyaline cartilage surrounded by a soft tissue joint capsule that maintains the constant contact of the cartilage surfaces. This joint capsule also maintains, within the joint, the synovial fluid that provides nutrition and lubrication of the joint surfaces. Ligaments are soft tissue condensations in or around the joint capsule that reinforce and hold the joint together while also controlling and restricting various movements of the joints. Ligaments, joint capsule, and connective tissue are largely comprised of collagen.
When a joint between two or more bones becomes unstable, either through disease or traumatic injury, its soft tissue or bony structures allow for excessive motion of the joint surfaces relative to each other and in directions not normally permitted by the ligaments or capsule. Sometimes there is simply a malaligmnent problem, as occurs with various unnatural positions of vertebrae in the spin. When one surface of a joint slides out of position relative to the other surface, but some contact remains, subluxation occurs. When one surface of the joint completely disengages and loses contact with the opposing surface, a dislocation occurs. Typically, the more motion a joint normally demonstrates, the more inherently loose is the soft tissue surrounding the joint. This makes some joints more prone to instability than others. The shoulder, glenohumeral joint, for example, has the greatest range of motion of all peripheral joints. It has long been recognized as having the highest subluxation and dislocation rate because of its inherent laxity relative to more constrained "ball and socket" joints such as the hip.
Patent applications from the laboratory of the inventors have previously addressed some issues relating to joint instability. See, for example, U.S. patent application Ser. Nos. 08/637,095 and 08/714,987 (these applications also provide a thorough explanation of temperature control and energy supply systems that can be used with the present invention). Instability of the shoulder can occur congenitally, developmentally, or traumatically and often becomes recurrent, necessitating surgical repair. In fact, subluxations and dislocations are a common occurrence and cause for a large number of orthopedic procedures each year. Symptoms include pain, instability, weakness and limitation of function. If the instability is severe and recurrent, functional incapacity and arthritis may result. Surgical attempts are directed toward tightening the soft tissue restraints that have become pathologically loose. These procedures are typically performed through open surgical approaches that often require hospitalization and prolonged rehabilitation programs.
More recently, endoscopic endoscope (arthroscopic) techniques for achieving these same goals have been explored with variable success. Endoscopic techniques have the advantage of being performed through smaller incisions, and therefor are usually less painful. Such techniques are performed on an outpatient basis, associated with less blood loss and lower risk of infection and have a more cosmetically acceptable scar. Recovery is often faster postoperatively than using open techniques. However, it is often more technically demanding to advance and tighten capsule or ligamentous tissue arthroscopically because of the difficult access to pathologically loose tissue, and because it is very hard to determine how much tightening or advancement of the lax tissue is clinically necessary. In addition, fixation of advanced or tightened soft tissue is more difficult arthroscopically than through open surgical methods.
Collagen connective tissue is ubiquitous in the human body and demonstrates several unique characteristics not found in other tissues. It provides the cohesiveness of the musculoskeletal system, the structural integrity of the viscera as well as the elasticity of integument. There are basically five types of collagen molecules, with Type I being most common in bone, tendon, skin and other connective tissues, and Type III is common in muscular and elastic tissues.
Intermolecular cross-links provide collagen connective tissue with unique physical properties of high tensile strength and substantial elasticity. A previously recognized property of collagen is hydrothermal shrinkage of collagen fibers when elevated in temperature. This unique molecular response to temperature elevation is the result of rupture of the collagen stabilizing cross-links and immediate contraction of the collagen fibers to about one-third of their original lineal distention. Additionally, the caliber of the individual fibers increases greatly, over four-fold, without changing the structural integrity of the connective tissue.
There has been discussion in the existing literature regarding alteration of collagen connective tissue in different parts of the body. One known technique for effective use of this knowledge of the properties of collagen is through the use of infrared laser energy to effect tissue heating. The importance in controlling the localization, timing and intensity of laser energy delivery is recognized as paramount in providing the desired soft tissue shrinkage without excessively damaging the surrounding non-target tissues.
Shrinkage of collagen tissue is important in many applications. One application is the shoulder capsule. The capsule of the shoulder consists of a synovial lining and three well-defined layers of collagen. The fibers of the inner and outer layers extend in a coronal access from the glenoid to the humerus. The middle layer of the collagen extends in a sagittal direction, crossing the fibers of the other two layers. The relative thickness and degree of intermingling of collagen fibers of the three layers vary with different portions of the capsule. The ligamentous components of the capsule are represented by abrupt thickening of the inner layer with a significant increase in well-organized coarse collagen bundles in the coronal plane.
The capsule functions as a hammock-like sling to support the humeral head. In pathologic states of recurrent traumatic or developmental instability this capsule or pouch becomes attenuated, and the capsule capacity increases secondary to capsule redundance. In cases of congenital or developmental multidirectional laxity, an altered ratio of Type I to Type III collagen fibers may be noted. In these shoulder capsules, a higher ratio of more elastic Type III collagen has been described. Shrinkage of capsule collagen to improve shoulder function was previously developed in the laboratory of the inventors.
Additionally, there are a number of skeletal disorders associated with malalignment of adjacent bones that are caused by either incorrect tension available from a ligament or from a group of separate ligaments, resulting either from disease or traumatic injury. Prior investigations into methods of tightening the capsule of the shoulder joint, an earlier focus of research in the laboratory of the present inventors, has shown a need for more focused research and improvements in methods of treating disorders associated with medically incorrect (under disease or post-traumatic conditions) ligament tension. The need for such further developments has led to the present invention.